In the code above there are 2 image buttons, that move between different ItemNum. Im trying to stop the user from clicking the previous button, by removing the imgbtnPrev button when the query string at 1.

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Dim number As Integer
If Request.QueryString("qryItemNum") IsNot Nothing Then
Dim isNumeric As Boolean = Integer.TryParse(Request.QueryString("qryItemNum").ToString(), number)
If isNumeric = True Then
If Convert.ToInt(Request.QueryString("qryItemNum")) <= 1 Then
imgbtnPrev = False
End If
End If
End If

I downvoted because there is no error checking. Non-numeric querystring value will bomb.... also wrong language.... and there are other problems that will keep it from compiling.
–
MikeSmithDevMar 1 '13 at 20:18

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Not Page.IsPostBack Then
imgbtnPrev = False
Dim qryItemNum As String = Request.QueryString("qryItemNum")
If Not String.IsNullOrEmpty(qryItemNum) Then
Dim ItemNum As Int32
If Int32.TryParse(qryItemNum, ItemNum) Then
imgbtnPrev = (-1 < ItemNum)
End If
End If
End If
End Sub

This assumes, of course, that imgbtnPrev is defined somewhere in your code or your ASPX page.

EDIT: From one of your comment imgbtnPrev.Visible = False to your original question, it appears that imgbtnPrev is a button on your form. If that is the case, you would write something like this:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Not Page.IsPostBack Then
imgbtnPrev.Visible = False
Dim qryItemNum As String = Request.QueryString("qryItemNum")
If Not String.IsNullOrEmpty(qryItemNum) Then
Dim ItemNum As Int32
If Int32.TryParse(qryItemNum, ItemNum) Then
imgbtnPrev.Visible = (-1 < ItemNum)
End If
End If
End If
End Sub

EDIT2: This version employs the Try...Catch to see what the error was:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Not Page.IsPostBack Then
imgbtnPrev.Visible = False
Try
Dim qryItemNum As String = Request.QueryString("qryItemNum")
If Not String.IsNullOrEmpty(qryItemNum) Then
Dim ItemNum As Int32
If Int32.TryParse(qryItemNum, ItemNum) Then
imgbtnPrev.Visible = (-1 < ItemNum)
End If
End If
Catch err As Exception
Response.Write(err.Message)
End Try
End If
End Sub